Which pairing correctly describes GPIb activation in vivo and in vitro?

Which pairing correctly describes GPIb activation in vivo and in vitro?

• A. Shear force and Ristocetin
• B. Ristocetin and compression
• C. Activation of ADP Receptor and Ristocetin
• D. Binding von Willebrand factor and Epinephrine

Answer: (A)

The key idea is how GPIb-IX-V engages von Willebrand factor to start platelet adhesion, with different triggers in vivo and in vitro. In the body, high shear forces in vessels cause von Willebrand factor to stretch and expose its binding site for GPIb, allowing platelets to tether to the injured surface. In the lab, ristocetin serves as a surrogate trigger: it promotes or stabilizes the interaction between von Willebrand factor and GPIb, leading to platelet clumping that reflects GPIb activation. So pairing shear force with ristocetin best captures GPIb’s activation in both environments. Other options don’t fit because they mix pathways that aren’t primarily about GPIb-vWF interaction. Ristocetin alone doesn’t describe in vivo shear-driven adhesion, compression isn’t a driver of GPIb engagement, and ADP receptor activation or epinephrine-related pathways involve different receptors and steps in platelet activation.

The key idea is how GPIb-IX-V engages von Willebrand factor to start platelet adhesion, with different triggers in vivo and in vitro. In the body, high shear forces in vessels cause von Willebrand factor to stretch and expose its binding site for GPIb, allowing platelets to tether to the injured surface. In the lab, ristocetin serves as a surrogate trigger: it promotes or stabilizes the interaction between von Willebrand factor and GPIb, leading to platelet clumping that reflects GPIb activation. So pairing shear force with ristocetin best captures GPIb’s activation in both environments.

Other options don’t fit because they mix pathways that aren’t primarily about GPIb-vWF interaction. Ristocetin alone doesn’t describe in vivo shear-driven adhesion, compression isn’t a driver of GPIb engagement, and ADP receptor activation or epinephrine-related pathways involve different receptors and steps in platelet activation.